Music theory is a field of study that describes the elements of music and includes the development and application of methods for analyzing and composing music, and the interrelationship between the music notation|notation of music and performance practice. Broadly, theory may include any statement, belief, or conception of music (Boretz, 1995). A person who studies or practices music theory is a music theorist.
Music theory generally attempts to reduce the practice of composing and playing into rules and ideas. In the Western tradition, the study of music theory stems from a belief that the acts of composing, performing, and listening to music are all based on traditions that may be explicated to a high degree of detail (this, as opposed to a conception of musical expression as fundamentally ineffable except in musical sounds). Generally, music theory works are both descriptive and prescriptive, that is they both attempt to define practice and to influence later practice. Thus, music theory generally lags behind practice in important ways, but also points towards future exploration and performance. Musicians study music theory in order to be able to understand the relationships that a composer or songwriter expects to be understood in the notation, and composers study music theory in order to be able to understand how to produce effects and to structure their own works. Composers may study music theory in order to guide their precompositional and compositional decisions. Broadly speaking music theory in the Western tradition focuses on harmony and counterpoint, and then uses these to explain large scale structure and the creation of melody.
Music theory describes how sounds, which travel in waves, are notated, and how what is sounded, or played, is perceived by listeners. The study of how humans interpret sound is called psychoacoustics, while the cognitive aspects of how perceived sounds are interpreted into musical structures is studied in music cognition. In music, sound waves are usually measured not by length (or wavelength) or period, but by frequency.
Every object has a resonant frequency which is determined by the object's composition. The different frequencies at which the sound producers of many instruments vibrate are given by the harmonic series. The resonators of musical instruments are designed to exploit these frequencies. Different instruments have different timbres because of variation in the size and shape of the instrument.
Sounds can be classified into pitches, according to their frequencies or their relative distance from a reference pitch. Tuning is the process of assigning pitches to notes. The distance in pitch between two notes is called an interval. Notes, in turn, can be arranged into different scales and modes. The most common scales are the major and minor scales.
Rhythm is the arrangement of sounds in time. Meter animates time in regular pulse groupings, called measures (or bars in British English). The time signature specifies how many beats are in a measure, and which kind of written note is counted and felt as a single beat. Through increased stress and attack (and subtle variations in duration), particular tones may be accented. There are conventions in most musical traditions for a regular and hierarchical accentuation of beats to reinforce the meter. Syncopated rhythms are rhythms that accent parts of the beat not already stressed by counting. Playing simultaneous rhythms in more than one time signature is called polyrhythm.
Melody is the unfolding in musical time of a principle single line. This line can be sounded alone, unaccompanied; or it can be the top (or sometimes an inner) note of a squence of chords, or sounded against chords as a background by accompanying instruments or voices. Melodic rhythm is usually rooted in the accent patterns of language, and/or the animating rhythms of dance steps and forms.
In much of Western music, melody is often the most identifiable theme. Melodies will often imply certain scales or modes. Counterpoint is the study of combining and layering more or less independent melodies.
Harmony, consonance, & dissonance
Harmony can generally be thought of as occurring when two or more pitches are sounded simultaneously, although harmony can be implied when pitches are sounded successively rather than simultaneously (as in arpeggiation). Harmonies involving three or more pitches sounded simultaneously are referred to as chords, though the term is generally used to indicate an organized selection of pitches rather than just any three or more pitches.
Consonance can be roughly defined as harmonies whose tones complement and augment each others' resonance, dissonance as those which create more complex acoustical interactions (called 'beats'). Another manner of thinking about the relationship regards stability; dissonant harmonies are sometimes considered to be unstable and to "want to move" or "resolve" toward consonance. However, this is not to say that dissonance is undesirable. A composition made entirely of consonant harmonies may be pleasing to the ear and yet boring because there are no instabilities to be resolved.
Brief audio (MIDI) musical examples of the interaction and effect of consonance and dissonance upon each other can be be found here: "The effect of context on dissonance'" and here: "The role of harmony in music"
Melody is often organized so as to interact with changing harmonies (sometimes called a chord progression) that accompany it, setting up consonance and dissonance.
Music notation is the graphical representation of music. In standard notation, pitches (notes) are represented on the vertical axis and time (rhythm) is represented as symbols on the horizontal axis. Together, these two components make up the musical staff, along with directions indicating the key, tempo, dynamics, etc.
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